The present invention relates generally to an electronic closed loop air-fuel ratio control system for use with an internal combustion engine, and particularly to an improvement in such a system for optimally controlling the air-fuel mixture fed to the engine by controlling a time constant of an integrator or a proportional constant of a proportional circuit of the system.
Various systems have been proposed to supply an optimal air-fuel mixture to an internal combustion engine to reduce noxious components of the emissions, one of which utilizes the concept of an electronic closed loop control system based on a sensed concentration of a component in exhaust gases of the engine.
According to the conventional system, an exhaust gas sensor, such as an oxygen analyzer, is deposited in an exhaust pipe for sensing the concentration of a component of exhaust gases from an internal combustion engine, generating an electrical signal representative of the sensed concentration of the component. A differential signal generator is connected to the sensor for generating an electrical signal representaive of a differential between the signal from the sensor and a reference signal. The reference signal is previously determined in due consideration of, for example, an optimum ratio of an air-fuel mixture to the engine for maximizing the efficiency of both the engine and an exhaust gas refining means. A so-called proportional-integral (p-i) controller is connected to the differential signal generator, receiving the signal therefrom, and generating a signal. A pulse generator is connected to the p-i controller receiving the signal therefrom, generating a train of pulses based on the signal received, which pulses are fed to an air-fuel ratio regulating means, such as electromagnetic valves, for supplying an air-fuel mixture with an optimum air-fuel ratio to the engine.
In the previously described conventional control system, however, a problem is encountered as follows. That is, the output of the proportional controller is undesirably changed depending upon engine speed change, with the result of the fact that the air-fuel ratio control can not be properly carried out. The reason why the engine speed change affects the output of the p-i controller is that the response transient of the system is not negligible. The above described defect of the prior art will be discussed in detail in connection with FIGS. 4a-4d of the accompanying drawings.